Electronic structure of Ge2 and Ge2− and thermodynamic properties of Ge2 from all electron ab initio investigations and Knudsen effusion mass spectroscopic measurements

Abstract The low-lying states of the molecule Ge 2 and of the ion Ge 2 − have been investigated by all electron ab initio multi-configuration self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations. The relativistic corrections for the Darwin contact term and for the mass–velocity term have been determined in perturbation calculations. Treatment of the spin-orbit coupling has been included. The ground state of Ge 2 is derived as 0 g + ( 3 Σ g − ) with equilibrium distance 2.422 A, and vibrational frequency 270 cm −1 . The spectroscopic constants of 15 excited states are presented. Thermal functions based on the theoretically determined molecular parameters were used to derive the thermodynamic properties of the Ge 2 molecule from new mass spectrometric equilibrium data. The literature value for the dissociation energy of Ge 2 has been re-evaluated. The recommended dissociation energy, D ∘ 0 (Ge 2 ), and enthalpy of formation, Δ f H ∘ 298.15 (Ge 2 ), in kJ mol −1 are 260.7±6.8 and 484.8±6.8, respectively.